This invention relates to a roof construction formed from multiple hyperbolic paraboloid units, and more particularly to a roof construction in which the multiple units are joined together at contiguous surfaces and are supported by both vertical members and horizontally disposed and tensioned or compressed members.
Roof constructions employing hyperbolic paraboloid units are known in the prior art. In fact, applicant is the inventor of a laminated hyperbolic paraboloid unit that is described and claimed in U.S. Pat. o. 3,653,166. The disclosure of the '166 patent is incorporated herein by reference and describes the unit that is preferred for use in this invention.
A hyperbolic paraboloid unit makes efficient use of materials by relying on form or shape for strength, rather than on mass or depth of bending members. Specifically, a hyperbolic paraboloid unit contains two sets of parabolic curves, which, in plan view, extend in the diagonal directions of the unit. One set of parabolas is concave downwardly and the other set in concave upwardly, and a uniform load on the unit is carried in the two diagonal directions by the series of parabolas. The set of parabolas that is concave downwardly carries its load in axial compression, as in an arch, while the set of parabolas that is concave upwardly carries its load in tension, as in a cable.
A hyperbolic paraboloid unit, or shell, can be divided into four quadrants; each quadrant having a shell field that includes the two sets of parabolas in the diagonal directions. Most preferably, the edges of each quadrant are provided with stiffening members, and the quadrants are connected together through the stiffening members to form the complete hyperbolic paraboloid unit.
For many small building constructions it may be practical to employ a single hyperbolic paraboloid unit for the entire roof span. This is the case when it is easy to ship the unit with at least the quadrants fully assembled. If the quadrants are complete it is a fairly easy matter to assemble the unit on site by merely connecting the quadrants together. However, it is not desirable to employ a single unit to form an entire roof span when the span is so large that it is impractical to ship the unit with at least the quadrants in a fully assembled state. On site completion of the quadrants is a difficult and time consuming task. In the latter discussed situation, it is preferred to form the span from multiple units that are of a size permitting easy shipment of fully assembled quadrants. It is also desirable to form a roof construction without using interior vertical supports. Obviously, by omitting such supports the area under the roof span will be unobstructed and can be most effectively utilized. Roof constructions that are free of interior vertical columns are referred to as "free span" roof constructions.
A free span roof construction formed of multiple hyperbolic paraboloid units is employed in the athletic facility at the Pratt Institute in Brooklyn, New York. This roof construction is primarily a three-hinged arch that depends upon long sloping compression struts to transmit the load from the interior area of the roof to peripheral vertical buttresses. Although the sloping strut arrangement creates a high vaulted interior, which may be desirable for some installations, it does so by transmitting a large horizontal component of load to the vertical buttresses. The heavy buttresses and strong foundation necessary to support these large loads are expensive to construct. Furthermore, the sloping struts are formed from heavy members because they are required to carry large loads, and these heavy struts are also quite expensive to use in roof construction. The roof construction of the present invention does not require the use of heavy sloping struts, and can employ lighter and less expensive vertical supports than those employed in the above described three-hinged arch arrangement.